Quick Answer: Use 2% salt by weight for most vegetable ferments - weigh the vegetables, multiply by 0.02, and that is your salt in grams. Spoon measurements fail because salt crystals differ in density by up to twice between types, so a tablespoon of coarse sea salt and a tablespoon of fine salt are not the same amount of salt at all. Below about 1.5% you get soft, slimy, or mouldy results. Above about 3.5% fermentation stalls. Nearly every home ferment failure sits outside that band.

The recipes are not lying to you, they are just written in a unit that does not survive the trip from one kitchen to another. Switching to percentages takes one extra minute and it is the difference between a reliable ferment and a coin flip.

Why does salt by volume fail so badly?

Because salt crystals vary enormously in size, and a spoon measures space rather than salt.

A tablespoon of fine table salt weighs roughly 18-20g. A tablespoon of coarse kosher salt weighs somewhere around 10-15g depending on the brand, because the large flakes pack with air between them. A tablespoon of flaky finishing salt can be under 8g.

So a recipe calling for a tablespoon of salt per kilo of cabbage delivers anywhere from 0.8% to 2% depending entirely on which box is in your cupboard. That range spans the difference between a slimy failure and a perfect kraut.

This single variable explains an enormous share of the reports where someone follows a recipe exactly and gets a different result from the person who wrote it. It is not the temperature, the water, or the jar. It is that the two of you own different salt.

The fix is a £10 kitchen scale. Weigh the vegetables, weigh the salt, and the recipe becomes portable across every kitchen and every brand.

What percentage should you actually use?

It depends on the vegetable and the season, and the useful range is narrower than you might expect.

2% is the default. Sauerkraut, most mixed vegetable ferments, kimchi after the brining stage. This is the figure to memorise.

2.5-3% for cucumbers, and anything you want to stay crunchy. Higher salt slows softening enzymes and keeps texture firm. Pickles are the classic case.

1.5-2% for a faster, tangier, softer result. Works well for shredded root vegetables and for anyone who finds standard kraut too salty. Ferment it at cooler temperatures and eat it sooner.

3-3.5% in warm conditions. This is the one that matters right now. In a kitchen above about 24C, go up half a percent - warmth speeds everything including the organisms you do not want, and the extra salt restores the balance. As the house cools through September, come back down.

Below 1.5%: unreliable. Slime, off smells, and surface mould become common. Above 3.5%: lactobacillus itself is inhibited. Fermentation slows to a crawl or does not start.

How do you calculate it, exactly?

Two methods, depending on whether you are making a dry-salted ferment or a brine.

Dry salting - for cabbage, kraut, anything that makes its own liquid.

Weigh your prepared vegetables in grams. Multiply by 0.02. That is your salt.

1,000g shredded cabbage x 0.02 = 20g salt. Massage in, wait 20 minutes, and it will draw enough liquid to submerge itself.

Brining - for cucumbers, carrots, beans, anything that stays whole.

Here you must include the water in the calculation, and this is where most people go wrong. Weigh the vegetables plus the water together, then take your percentage of that total.

500g cucumbers + 700g water = 1,200g total. x 0.025 = 30g salt.

Dissolving the salt in the water first gives a more even distribution. Use non-iodised salt - iodine inhibits some of the bacteria you want, and anti-caking agents cloud the brine.

Write the percentage on the jar lid in marker. In six weeks you will not remember, and knowing what worked is how you get better at this.

5 Mistakes Everyone Makes With Fermenting Salt

1. Weighing the vegetables before trimming. Weigh what actually goes in the jar - after coring, peeling, and discarding. A cabbage core is 15% of the weight and none of it is being fermented.

2. Forgetting the water in a brine. Calculating 2% of the vegetables alone and then adding 700g of water gives you an actual brine strength closer to 1%. This is the single most common brine failure and it produces exactly the soft, cloudy, off-smelling result people describe.

3. Using iodised table salt. Iodine is antimicrobial - that is the point of it - and it inhibits the lactobacillus you are trying to encourage. Any non-iodised salt works: sea salt, kosher, pickling salt, plain rock salt.

4. Adjusting for taste mid-ferment. Adding salt to a running ferment shocks the culture, and adding water dilutes it below the safe range. Decide at the start.

5. Using the same percentage all year. A 2% kraut in a 26C August kitchen and a 2% kraut in an 18C October kitchen are two different processes. The percentage should move with the temperature, and this is the adjustment that turns an occasional success into a reliable one.

What does the wrong percentage actually look like?

The failures are distinctive enough to diagnose after the fact, which is useful for the next batch.

Too little salt gives you: liquid that turns cloudy and slightly viscous within days, a soft or mushy texture, a smell that is more rotten than sour, and surface mould appearing early. Slimy brine specifically - the kind that strings when you lift the weight - is the classic under-salting signature.

Too much salt gives you: almost nothing happening. No bubbles after four or five days, no souring, and vegetables that stay stubbornly raw-tasting and firm. It is not dangerous, it is just stalled, and it is recoverable - dilute the brine slightly with unsalted water and give it warmth.

The right amount gives you: visible bubbles within 2-4 days at room temperature, brine that stays relatively clear or goes faintly cloudy, a clean sour smell developing by day three, and a pH dropping below 4.6 within about a week.

One thing that is normal and alarms people: a white film on the surface is usually kahm yeast, which is harmless and can be skimmed. Fuzzy growth in any colour is mould, and that batch goes in the bin.

FAQ: Fermentation Salt Questions, Answered

Can I reduce the salt for health reasons?

You can go to 1.5% safely with good technique and a cool room. Below that the safety margin narrows meaningfully. A better approach is to keep 2% and eat smaller portions - a 30g serving of kraut is not a significant sodium source.

Does the salt type change the flavour?

Mildly. Sea salt with trace minerals gives a slightly rounder flavour than pure sodium chloride. The difference is small compared to temperature and time.

My kitchen swings from warm days to cold nights. What percentage?

Use the daytime high to set your percentage, since that is when fermentation runs fastest. In a kitchen hitting 25C by afternoon, go 2.5% even if the nights are cool.

TL;DR:

• Weigh, do not spoon. Salt density varies by up to double between types, which is most of the difference between recipes that work and ones that do not.
• 2% by weight is the default. 2.5-3% for crunch, up half a percent in a warm kitchen.
• For brines, include the water in the total weight - forgetting this is the most common failure.
• Slimy and cloudy means too little salt. Nothing happening means too much.

One scale and one multiplication turns fermenting from a folk art into something reproducible. It is the cheapest upgrade available in any kitchen.